A 1979 musical film set in the 1950s starring John Travolta as the leader of a high school gang and Olivia Newton-John as the girl-next-door love interest. Adapted from a Broadway musical, the movie and its soundtrack were blockbusters hits. If you watched the live version on TV in 2016, you already know the ending.
If you didn’t, sorry, I’m not including a video. Go rent it. It’s worth it.
Just keep in mind that in those days, adults actors in their 20s and 30s were casted to play play teenagers. Casting teens to play teens is actually a recent phenomenon. I can’t tell you why.